1. Field of the Invention
The present invention relates to a scrolling apparatus for repositioning an image relative to a display screen. More particularly, the present invention relates to a high resolution scrolling apparatus that may be incorporated into an input device, such as a mouse, trackball, or keyboard, to scroll an image relative to a display screen.
2. Description of Background Art
The viewable contents of a computer file, such as a text document, spreadsheet, digital photograph, Web page, or other image rendered on a conventional display screen, may possess a size exceeding the viewable boundaries of the display screen. To address this issue, an individual may utilize a scrolling apparatus to reposition the image relative to the display screen, thereby permitting the individual to view portions of the computer file not currently rendered. As utilized herein, scrolling describes a translatory movement of the image relative to the display screen and in a particular direction. For example, scrolling down generally describes a movement of the image relative to the display screen so as to produce an effect of moving downward in the image. Similarly, scrolling up, scrolling left, and scrolling right generally describe movement of the image relative to the display screen so as to produce an effect of moving the image upward, left, and right, respectively.
Scrolling apparatuses have been incorporated into a plurality of peripheral input devices, including computer mice and trackball pointing devices, for example. An example of a computer mouse incorporating a scrolling apparatus is disclosed in U.S. Pat. No. 5,912,661 to Siddiqui, which is hereby incorporated by reference. Elements of the scrolling apparatus include a finger-engageable scroll wheel and a sensor assembly. The scroll wheel is mounted within a housing of the computer mouse, and a portion of the scroll wheel protrudes from an opening in the housing to permit an individual to selectively rotate the scroll wheel. The sensor assembly detects rotation of the scroll wheel and transmits a corresponding signal to a host computer, thereby directing the image to scroll relative to the display screen. By rotating the scroll wheel in a first direction, an image on a display screen may be scrolled upward, for example. Similarly, by rotating the scroll wheel in an opposite second direction, the image may be scrolled downward. Accordingly, a scroll wheel may be operated in a bi-directional manner to vertically scroll the image relative to the display screen.
The sensor assembly in U.S. Pat. No. 5,912,661 includes an encoder wheel, a light source, and a light sensor. The encoder wheel and the scroll wheel are spaced from each other and mounted in an axially-aligned manner on a shared rotatable axle that is positioned within the housing. In addition, the encoder wheel is positioned between the light source and the light sensor. A plurality of angularly-spaced openings extend around a periphery of the encoder wheel to form a circular sensing region. As the encoder wheel rotates, light from the light source is alternately (1) transmitted through the openings and (2) blocked by the material of the encoder wheel. As the encoder wheel rotates, the pulses of light transmitted through the openings are detected by the light sensor. In response to the pulses of light, the light sensor transmits a signal to a host computer that indicates rotation of the scroll wheel, thereby inducing scrolling of the image relative to the display screen. Furthermore, the frequency of the sensed pulses corresponds to the rate at which the scroll wheel is being rotated. Accordingly, the rate at which the scroll wheel rotates is generally correlated to the speed at which the image scrolls.
In another existing scrolling apparatus, the scroll wheel includes, in the form of a hub, a plurality of internal angular slit openings that form an encoder disk/wheel. The light source and the light sensor are positioned on opposite sides of the encoder wheel. When the scroll wheel is rotated, light pulses are alternatively (1) transmitted through the openings and are detected by the light sensor, and (2) blocked by material between the slits. Scrolling is then performed similar to the manner described above.
In each scrolling apparatus discussed above, the scroll wheel and the encoder wheel rotate at the same rate. That is, a single rotation of the scroll wheel causes a single rotation of the encoder wheel. The sensing capabilities of these embodiments therefore depend upon the number of openings or slits in the encoder wheel at its sensing radius location. For example, if there are 20 openings disposed on the encoder wheel (1 opening for every 18°), a single rotation of the scroll wheel will cause the encoder wheel to rotate a full 360° and there will be 20 pulses. To increase the resolution capabilities of the described systems, the encoder wheels would need to be provided with more openings or slits that are spaced closer together so that more pulses are provided per revolution. However, there is a practical limit in increasing the number of openings in an encoder wheel with a limited sensing diameter due to manufacturing capabilities, tolerances, and costs. Accordingly, a scroll wheel sensing arrangement with increasing resolution capabilities was thus needed.